1. Field of the Invention
The present invention relates to a zinc-modified ferritic stainless steel and manufacturing method thereof, in particular a zinc-modified ferritic stainless steel with a decent capacity of corrosion resistance and manufacturing method thereof. Its chemical components (by weight percent, wt %) comprise chromium being in a range of 14-16 weight percent, zinc being in a range of 0.001-4 weight percent, nitrogen being in a range of 0.001-0.02 weight percent, carbon being in a range of 0.003-0.015 weight percent, and rest of weight percentage of compositions being iron and a few amount of inevitable impurities.
2. Description of the Related Art
Currently, the commercial stainless steels could be classified as one of the four types: austenite, ferrite, martensite and precipitation-hardening. Based on the theory, chromium should occupy at least 12 weight percent of the components in the whole types of stainless steels to form a complete protective film for achieving the stainless effect.
In the stainless steels mentioned above, because the nonmagnetic 300 series of austenitic stainless steels contain a better working capacity and a corrosion resistance, the quantity of their usage is the largest and they are broadly applied in the fields of staple merchandise, machine parts of food and medical tools. A common 300 series of austenitic stainless steels comprise nickel in the range of 6-12 weight percent, and nickel is an important element for stabilizing the austenitic stainless steels which are easily worked and improving the capacity of corrosion resistance. However, among the main elements including iron, chromium and nickel composing the stainless steels, the price of nickel is the highest and it fluctuates extremely. Additionally, nickel is one of the strategic materials. Therefore, in order to reduce the amount of nickel applied to the stainless steels, the 200 series of austenitic stainless steels with few amount of nickel in content gradually draw lots of attention from the manufacturers of the stainless steels in recent years. These stainless steels are made of three cheap elements including manganese, nitrogen and carbon to replace parts of nickel in content. Generally, the experience shows 1 weight percent of nickel is replaced by 2 weight percent of manganese. For example, adding chromium in a range of 16-18 weight percent, manganese in a range of 5.5-7.5 weight percent, nickel in a range of 3.5-5.5 weight percent, carbon below 0.15 weight percent and nitrogen below 0.25 weight percent into iron for steel number AISI 201; adding chromium in a range of 17-19 weight percent, manganese in a range of 7.5-10 weight percent, nickel in a range of 4-6 weight percent, carbon below 0.15 weight percent and nitrogen below 0.25 weight percent into iron for steel number AISI 202; adding chromium in a range of 15-17 weight percent, manganese in a range of 7-9 weight percent, nickel in a range of 1.5-3 weight percent, carbon below 0.03 weight percent and nitrogen in a range of 0.15-0.3 weight percent into iron for steel number AISI 204; adding chromium in a range of 16.5-18 weight percent, manganese in a range of 14-15.5 weight percent, nickel in a range of 1-1.75 weight percent, carbon below 0.25 weight percent and nitrogen below 0.4 weight percent into iron for steel number AISI 205. Only the steel numbers mentioned above in the 200 series of stainless steels should be added with nickel for stabilizing the austenitic iron. And the magnetic series of ferritic stainless steel within the other four types, for example, AISI 430, although their contents do not contain any nickel, the corrosion resistance of them is poor so that they are limited in applications.
Therefore, in order to achieve the goal of manufacturing the series of austenitic stainless steels without nickel in content, the manufacturer can try the method of adding manganese, nitrogen or carbon into the content again or other technique such as reducing the content of chromium and so on to achieve the goal of manufacturing the stainless steels without nickel. However, in prior art, if there is too much content of manganese or carbon in the stainless steel, adverse effects are easily generated in hot work or the capacity of resisting corrosion of the stainless steel. Therefore, when using manganese or carbon to replace nickel, the amount thereof should be limited.
Currently, the commercial series of austenitic stainless steels without nickel in content such as steel number UNSS 28200, adding chromium in a range of 17-19 weight percent, manganese in a range of 17-19 weight percent, copper in a range of 0.5-1.5 weight percent, molybdenum in a range of 0.5-1.5 weight percent, nitrogen in a range of 0.4-0.6 weight percent, and carbon below 0.15 weight percent into iron for it. This kind of stainless steel contains chromium much more. Although adding elements such as molybdenum, manganese and so on could achieve the goal of manufacturing the series of austenitic stainless steels without nickel in content; these elements have the shortcoming of high price.
Therefore, based on the aforementioned problems in the prior art technique, the objective of the present invention is to provide a novel zinc-modified ferritic stainless steel corresponding to the basic requirement of keeping its high capacity of corrosion resistance together with lowering the addition of elements with high price such as chromium, manganese, molybdenum, and so on for reducing the production cost of the stainless steel with high capacity of corrosion resistance.